Studies On The Pretreatment Of Rice Straw By Mild Alkaline Hydrogen Peroxide Combined With Ionic Liquid-water Mixtures And Recycle Of Ionic Liquid

With the shortage of global fossil fuel supply and the increasing environmental deterioration resulted from the use of fossil fuel,it is urgent to find alternative and renewable energy resources.Lignocellulosic wastes represent the most abundant renewable biomass on earth,among which rice straw?RS?,as one of the most abundant and attractive lignocellulosic wastes,has great potential of biofuels production.However,owing to its compact recalcitrant structure,raw RS is very hard to be degraded directly.Hence,an effective pretreatment is required to improve the degradability of RS by breaking the seal of lignin and hemicellulose to cellulose.In recent years,ionic liquid?IL?pretreatment of lignocellulose has attracted a lot of attention,as ILs have unique natures such as high thermal and chemical stability,environment-friendliness,the ability to dissolve many kinds of substances,and can be recycled and reused.In this study,the feasibility of mild alkaline hydrogen peroxide combined with IL-water mixtures to pretreat RS had been investigated.The pretreatment effect was evaluated,and the mechanisms of pretreatment was investigated by a series of characterization methods.On this basis,the effect of fed-batch modes on enzymatic hydrolysis and the ethanol production through utilization of Saccharomyces cerevisiae at high solid loading had been explored.Moreover,the recycle and reuse of IL had been fully studied.The optimized conditions of mild alkaline hydrogen peroxide pretreatment consisted of 3%?w/w?of H₂O₂,15%?w/v?of RS loading,11.5 of pH,30°C of pretreatment temperature,and2 h of pretreatment time.The mild alkaline peroxide pretreatment combined with[Bmim]Cl-water mixtures pretreatment at a optimal water content of 30 wt%could significantly raise the enzymolysis efficiency and fermentation efficiency of RS to 92.1%and 91.0%,respectively.The alkaline peroxide pretreatment could remove part of lignin through the oxidation of free radical and destroy the RS structure to boost the dissolution of amorphous components by the[Bmim]Cl-water mixtures,leading to a maximum lignin removal of 63.8%,and the crystallinity index was increased from 29.2 to 46.8.The properties of enzymolysis and fermentation of pretreated RS at high solid loadings were explored.The effect of reducing the enzyme loading on enzymolysis and the enzymatic hydrolysis with different feeding modes were investigated.In the process of enzymolysis,the RS with combined pretreatment could still maintain a good enzymolysis when the enzyme loading was reduced.Under the high solid loading of 30%?w/v?,the enzyme feeding mode could improve the reducing sugar productivity of enzymolysis of pretreated RS.At 48 h of enzymatic hydrolysis,the reducing sugar concentration under enzyme feeding mode could reach 147.4 g/L,while the batch mode only with 127.2 g/L.Simultaneous saccharification co-fermentation?SScF?and separate hydrolysis fermentation?SHF?at high solid loading were also studied,and the results showed the SScF was superior to SHF.SScF at different solid loadings was performed.With the improvement of solid loading,the ethanol concentration achieved 91.9g/L,and the production of succinic acid increased with the increasing ethanol production,showing a linear correlation between them.The addition of different concentration of succinic acid could not change the metabolic flow to more ethanol to enhance the ethanol production.Investigation was also carried on recycle and reuse of IL.The RS pretreated with IL of different reuse cycles was investigated by component,enzymolysis and various characterization analysis.The results indicated that the residual K₃PO₄ alkali salt in the recycled IL led to further partial delignification during the pretreatment,and the improvement of enzymolysis efficiency of RS.Besides,RS pretreated with IL at 8-cycles reuse could still maintain high enzymolysis efficiency?98.9%?,which further proved the feasibility of the established combined pretreatment.